Q: battery loses charge fast after OS X Yosemite 10.10.3 update

Reinstalling OS X Without Erasing the Drive

Boot to the Recovery HD: Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

Reinstalling OS X Without Erasing the Drive

Repair the Hard Drive and Permissions: Upon startup select Disk Utility from the main menu. Repair the Hard Drive and Permissions as follows.

When the recovery menu appears select Disk Utility and press the Continue button. After Disk Utility loads select the Macintosh HD entry from the the left side list.  Click on the First Aid tab, then click on the Repair Disk button. If Disk Utility reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit Disk Utility and return to the main menu.

Reinstall OS X: Select Reinstall OS X and click on the Continue button.

Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless.

Alternatively, see:

Reinstall OS X Without Erasing the Drive

Choose the version you have installed now:

OS X Yosemite- Reinstall OS X

OS X Mavericks- Reinstall OS X

OS X Mountain Lion- Reinstall OS X

OS X Lion- Reinstall Mac OS X

     Note: You will need an active Internet connection. I suggest using Ethernet

                 if possible because it is three times faster than wireless.

I also noticed a significant drop in battery performance after 10.10.3. I am unclear as to your response Kappy. Are you suggesting that Apple's mechanism for updating the OS (via Software Update) is not the way in which users should update? How does what you provided affect battery performance?

Please review this Apple article:

Runaway applications can shorten battery runtime, affect performance, and increase heat and fan activity - Apple Support

For OS 10.9 and 10.10, you need to do something slightly different in the important Step 3. Starting with OS 10.9 the setting to view "All Processes" was moved to Activity Monitor's "View" menu:

Also not noted is that this test is not as effective if you run it immediately after a computer restart. Use the computer normally for  about a day, then run the test.